8. They become very slow and bury themselves in the mud. This process is called hibernation.

9. During the process of reproduction fertilized egg is changed into adult passing through a number of physical changes. This process is called metamorphosis.

10. The fertilized egg develops into larva. The larva of frog is called Tadpole. It has tail and gills. This larva later changes into adult.

CLASS REPTILIA

The animals of this class are called reptiles. They have following features.

REPTILES:

1. Most of the reptiles are terrestrial and only a few five in water.

2. They are also called crawlers.

3. They have thick, dry and rough skin.

4. The skin is covered with scales which originate from the ectoderm.

5. There are present lungs for respiration.

6. Teeth are present in their buccal cavity, which are used for cutting and biting.

7. The locomotary organs are legs but snakes and a few types of lizards have no legs.

8. Most of the lizards are not poisonous except members of the genus Heloderma which are found in American desert.

9. All the reptiles lay their eggs on land. Water dwelling reptiles e.g. turtle also lay their eggs on land.

10. Their eggs have a tough outer shell of calcium carbonate.

CLASS AVES

The animals included in this class are called Birds. Their distinguishing characters are as follows.

1. Birds have a single unique feature, which makes them different from other animals which is the presence of feathers. Their forelimbs are modified to form wings while hind limbs help in walking, wading and sitting on the branches.

2. All the birds have horny beaks without teeth.

3. All the birds lay eggs.

4. All the birds must have two wings for support and propulsion, strong but light and hollow bones.

5. Their digestive system is able to digest high caloric food.

6. They have a higher blood pressure and higher metabolic rate.

7. Nervous system and especially eye sight is very well developed so that they can track their path even at a very high speed.

· Glands:

· Skeleton:

Two occipital condyles, secondary bony palate, three bones in middle ear and fused pelvic bones and seven cervical vertebrae are present in their skeleton.

· External Ear:

Fleshy external ears are present in mammals.

· Eyelids:

Moveable eyelids are present in mammals.

· Teeth:

Two sets of teeth are present. Milk teeth are replaced by permanent set of teeth.

· Brain:

Brain is highly developed. It performs more functions than that of other vertebrates.

· Cranial Nerves:

Twelve pairs of cranial nerves are present.

· Circulatory System:

Circulatory system has four chambered heart, persistent left aorta and non-nucleated biconcave red blood corpuscles are present in female.

· Sexes:

Sexes are separate i.e. there are two individuals, male and female.

· Fertilization:

Most of them have internal fertilization and fetus developed inside the uterus of female giving birth to their children.

· Breast Feeding:

They feed the children by milk from mammary glands.

· Endothermic:

They are endothermic i.e. they can maintain their body temperature according to the environment. It means that they are warm-blooded animals.

Egg Laying Mammals

These mammals lay eggs. Mostly two eggs are laid in one year. Fertilization of egg is internal i.e. inside the body of mother. Eggs are laid in burrows of animals. Young ones are hatched from the eggs. Mother feed their children with milk. Their egg laying character shows their relationship with reptiles. Duck bill platypus and Spiny ant eater are the examples of egg laying mammals.

Pouched Mammals or Marsupial Mammals

These mammals have a pouch outside the belly called marsupium, this is the reason that they are also known as Marsupial mammals.

1. Fertilization of eggs and development of embryo is internal.

2. The embryo is at first encapsulated by shell membrane and floats free for several days in the uterine fluid.

3. There is no placenta.

4. After hatching from the shell membranes, the embryo does not implant or “take root” in the uterus and absorb nutrient secretions from the vascularized yolk sac.

5. The gestation period is brief and the marsupials give birth to tiny young that is effectively still an embryo.

6. These young creeps into the marsupium where it gets milk from mother through nipple.

7. It lives in marsupium until it can take care of itself.

8. Examples are Kangaroo, Koala, Tasmanian wolf and Wombat etc. These are found in Australia and Tasmania, Opossum is found in America. It lives on trees.

Placental Mammals

This is common group of mammals in which embryo completes its development inside the mother’s uterus. After gestation period young ones are born. Embryo remains in the uterus and gets its nourishment from mother through umbilical cord and placenta. Gestation period of these mammals is longer than those of other mammals. Pregnancy is called Gestation Period. In man it is of 9th months.

In mice it is 21 days, in rabbit 30 to 36 days, in cats and dogs 60 days, in cattle 250 days and in elephants 22 months. It is lengthier in large mammals.

The conditions of young ones at time of birth are different in different mammals. For example in antelope, at the time of birth, the body of young is covered over, with heavy fur, eyes are open and it can walk about. In case of rat, young is very weak, eyes are closed and has no hair on the body.

FLORA AND FAUNA OF PAKISTAN

Flora

“Different types of plans present in a particular region constitute its flora.”

Details

1. Hilly regions of Pakistan have snow fall and low temperature. These regions have thick forests where trees of Juniper (Sanober), Cedar, Chir, Chalghoza, Olive Apple, Plum Peach and Loqaut are very common.

2. Plain areas of Pakistan have fertile and less fertile soils. In areas where rainfall is low, desert environment is present in which Aeacia (Babool), Kikar, Ber, Pilas etc grow.

2. Many animals are used as food e.g. prawns, crabs and fish etc. Our rivers are rich in fish life particularly Rohu, Khagga, Malhi, Trout, and carps are abundant and used as human food, as well as a source of earning lively hood.

3. Frogs and toads are abundant.

4. The tortoises, turtles, snakes, crocodiles are also common.

5. On the plains of Pakistan we have very rich wild life. There is a great diversity of land fauna starting from earthworms, almost all kinds of insects, spiders, myriapods, snails, slugs to toads, lizards, snakes and enormous variety of birds and mammals.

6. Some of the birds peculiar to Pakistan are Houbara bustard, partridge, pheasant, falcons etc.

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